I discovered a tip, kind of by accident, for getting rid of them once and for all. (may not be a new tip to you but it was for me
) I've set the vinegar traps but they rarely worked. I heard they like to lay eggs in the slimy parts of your drain, like your garbage disposal if you don't have fruit out for them to lay eggs on.
So, with water running into your garbage disposal, turn on your disposal. With the disposal running, squirt a little dish soap down your disposal. With the the other side of your sink open, bubbles will spill out into the other side. Let the disposal run until the bubbles on the other side stop expanding. Then turn off and rinse. This is also a cheap way to clean your disposal without buying the expensive packets (same thing), and if you do it once a week it will get rid of the fruit flies. YAY!!!